Recent advances in the development of semiconductor and organic light-emitting diodes (LEDs and OLEDs) have made these devices suitable for use in general illumination applications, including architectural, entertainment, and roadway lighting, for example. As such, these devices are becoming increasingly competitive with light sources for example, incandescent, fluorescent, and high-intensity discharge lamps.
Optical feedback for a lighting system can be accomplished using a dedicated optical sensor, for example, a photodiode, phototransistor, or other similar device. U.S. Pat. No. 6,495,964 discloses a technique for using such a dedicated photosensor in an LED lighting system to allow for optical feedback and control of the mixed light by sequentially turning one colour of LED off and measuring the remaining light. There are commercial sensors with up to three separate colour channels to enable simultaneous measurements of both light intensity and relative spectral power distribution of incident light. The presence of these external sensors however, requires spectrally selective filters and optics to block or focus light onto the sensor. This type of configuration can lead to a complex, expensive and large hardware assembly for a lighting system.
It is known to those familiar with the art that light-emitting diodes may be used as photodiodes in either an unbiased photovoltaic mode or a reverse-biased photoconductive mode. Further, the responsivity of said photodiodes is determined by their junction areas. Consequently, LED's commonly referred to as “high brightness” light-emitting diodes (HBLEDs) with large junction areas typically feature high responsivities to incident radiant flux. It is also known that the intensity of HBLEDs can be controlled using Pulse Width Modulation (PWM), Pulse Code Modulation (PCM), or similar techniques wherein the drive current to the diodes can be periodically interrupted or pulsed.
Mims III, Forrest, “Sun Photometer with Light-Emitting Diodes as Spectrally Selective Detectors,” Applied Optics 31, 6965-6967, 1992, discloses a technique for using an LED as a spectrally selective detector in a sun photometer for atmospheric measurements. Mims suggests the use of different colours of LEDs exclusively as sensors to measure the light from the sun over a spectral range of 555 nm to 940 nm in the near infrared range, wherein each different colour of LED responds maximally to a different portion of the spectrum. This method of detection however, does not cover the visible spectrum well, which is approximately 400 nm to 700 nm and typically can only measure externally produced light. In addition, Mims describes the spectral responsivity of the LEDs used as being approximately as narrow a band as the emission spectra of the LEDs and therefore each device may detect essentially only a single colour of light.
U.S. Pat. No. 4,797,609 discloses a technique for using unenergized LEDs to monitor the light intensity of adjacent energized LEDs in an array of identical LEDs by directly measuring the current generated in the unenergized LEDs. In practice, the current generated by an LED exposed to light is on the order of microamps, which can be difficult to measure. Without high precision measuring devices and good filtering techniques, these forms of measurements can have a limited useful range.
U.S. Pat. No. 6,617,560 provides a lighting control circuit having an LED that outputs a first signal in response to being exposed to radiation together with a detection circuit coupled to the LED. The detection circuit generates a second signal from the first signal, which is subsequently delivered to a driver circuit that generates a third signal in response thereto. This third signal provides a means for controlling the illumination level of one or more LEDs to which the lighting control circuit is coupled. The configuration of this lighting control circuit defines the use and operation of these LEDs in a photocurrent mode, which enables them to operate solely as light detectors.
Therefore, there is a need for a new system and method for providing photonic emission and detection using light-emitting elements.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.